>  .  I  • 


U.S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU   OF   ENTOMOLOGY     CIRCULAR   No.   17* 

U  O    MOM  AKI>.  I  ninmolosi.i  iad  (  h.n  ol  Bnu 


ARSENATE  OF  LEAD  AS  AN  INSECTICIDE 
AGAINST  THE  TOBACCO  HORNWORMS. 


BT 


A.  C.  MORGAN   \m>  D.  C.  PARMAX, 
Entomtlofical  Assistant*. 


M047*— 18 


.TON  ;  OOVMNMtST   mihTINO  Of'ICt       '•'! 


BUREAU  OF  ENTOMOLOGY. 

L.  O.  Howard,  Entomologist  and  Chief  of  Bureau. 

C.  L.  Marlatt,  Entomologist  and  Acting  Chief  in  Absence  of  Chief. 

R.  S.  Clifton,  Executive  Assistant. 

W.  F.  Tastet,  Chief  Clerk. 

F.  H.  Chittenden,  in  charge  of  truck  crop  and  stored  product  insect  investigations. 

A.  D.  Hopkins,  in  charge  of  forest  insect  investigations. 

W.  D.  Hunter,  in  charge  of  southern  field  crop  insect  investigations. 

F.  M.  Webster,  in  charge  of  cereal  and  forage  insect  investigations. 

A.  L.  Quaintance,  in  charge  of  deciduous  fruit  insect  investigations. 

E.  F.  Phillips,  in  charge  of  bee  culture. 

D.  M.  Rogers,  in  charge  of  preventing  spread  of  moths,  field  work. 
Rolla  P.  Currie,  in  charge  of  editorial  work. 
Mabel  Colcord,  in  charge  of  library. 

Southern  Field  Crop  Insect  Investigations. 
W.  D.  Hunter,  in  charge. 

W.  D.  Pierce,  J.  D.  Mitchell,  G.  D.  Smith,  E.  A.  McGregor,  Harry  Pinkus. 

B.  R.  Coad,  W.  A.  Thomas,  R.  W.  Moreland,  A.  W.  Jobbins-Pomeroy,  C.  E. 

Hester,  engaged  in  cotton-boll  weevil  investigations. 
A.  C.  Morgan,  G.  A.  Runner,  S.  E.  Crumb,  D.  C.  Parman,  engaged  in  tobacco 

insect  investigations. 

F.  C.  Bishopp,  A.  H.  Jennings,  H.  P.  Wood,  W.  V.  King,  engaged  in  tick  investi- 
tions. 

T.  E.  Holloway,  E.  R.  Barber,  engaged  in  sugar-cane  insect  investigations. 

J.  L.  Webb,'  engaged  in  rice  insect  investigations. 

R.  A.  Cooley,  D.  L.  Van  Dine,  A.  F.  Conradi,  C.  C.  Krumbhaab,  collaborators. 

(ii) 


fci 


Circular  No.  173. 

United  States  Department  of  Agriculture, 

BUREAU    OF    ENTOMOLOGY. 
L.  O.   HOWARD,   Entomologiat  and  Chief  of  Bureau. 


ARSENATF,  OF  LEAD  AS  AN  INSECTICIDE  AGAINST  THE 
TOBACCO  BOBNWORMS. 

By  A.  <".   MnwiAN   :md   I).  C.   I'armaN, 
Entomological  AltistOntt. 

IN TKODUCTOKY. 

During  the  past  five  years  the  Bureau  of  Entomology  has  been 
conducting  an  investigation  of  tobacco  insects  in  Tennessee  and 
Kentucky  and  in  some  of  the  adjoining  States.  In  Tennessee  the 
bureau  has  been  very  materially  assisted  by  Prof.  H.  A.  Morgan, 
director  of  the  Tennessee  Agricultural  Experiment  Station. 

In  the  dark-tobacco  districts  of  Kentucky  and  Tennessee  tobacco 
hornworms  are  the  ever-present  and  most  serious  problem  of  the 
tobacco  grower,  Ten  to  twelve  years  ago,  when  labor  was  plentiful, 
•heap,  and  efficient,  "hand-worming"  was  found  to  be  economical 
and  effective  in  combating  this  pest  However,  during  the  last  six  or 
eight  years  hand-worming  has  become  too  costly,  because  of  the 
ivity  of  labor,  and  too  inefficient,  and  the  growers  have  been 
forced  to  employ  an  insecticide.  At  the  time  insecticides  were  first 
used  Paris  green  was  found  to  be  the  safest  and  most  efficient.  Nev- 
ertheless, there  has  always  l>oen  complaint  of  frequent  serious  burn- 
ing of  tobacco  as  a  result  of  its  use.  To  find  a  safe  and  effective 
insecticide  has  been  one  of  the  main  lines  of  investigation  by  the 
writers  during  the  past  five  years.  Di-plunihic  arsenate  of  lead  has 
been  found  to  meet  the  requirements.  In  the  further  discussion  of 
this  subject  the  use  and  action  of  Pari-  green  will  be  rather  thor- 
oughly discussed  in  connection  with  the  use  and  action  of  arsenate 
of  lead,  for  the  reason  that  since  the  insecticida]  results  of  the  use  of 
green  are  so  well  known  it  will  be  easier  to  explain  the  value 
of  arsenate  of  lead  if  it  be  compared  with  this  well-known  poison. 
1 


J 


2  ARSENATE   OF   LEAD   AGAINST   TOBACCO   HOKNWORMS. 

NECESSITY  AND  ADVANTAGES  OF  THE   USE   OF  AN   INSECTICIDE. 

The  way  in  which  the  scarcity  of  labor  tended  to  bring  about  the 
use  of  an  insecticide  upon  tobacco  has  already  been  explained.  In 
addition  to  this  necessity  of  using  insecticides,  the  much  greater 
efficiency  of  a  good  application  of  an  insecticide  is  another  strong 
argument  in  its  favor.  Hand-worming,  even  of  the  best,  has  many 
objections;  for  instance,  eggs  are  not  picked  off,  many  small  worms 
are  overlooked  on  account  of  their  small  size,  and,  lastly,  during  the 
hot  hours  of  the  day  large  worms  crawl  down  into  the  "  ruffles  "  near 
the  bases  of  the  leaves  and  a  considerable  number  are  thus  over- 
looked. On  the  other  hand,  a  thorough  application  of  an  insecti- 
cide will  kill  practically  every  hornworm — except  those  very  nearly 
full  grown — within  two  or  three  days,  and  will  also  continue  to  kill 
the  young  worms  that  hatch  several  days  after  the  application.  In 
short,  hand-picking  has  only  an  immediate  effect  in  lessening  the 
worms,  whereas  the  application  of  an  insecticide  usually  continues  to 
kill  over  a  period  of  several  days.  Cheapness  is  another  point  very 
greatly  in  favor  of  an  insecticide  as  compared  with  hand-picking. 
The  cost  of  keeping  an  acre  of  tobacco  hand-wormed  in  a  year  when 
worms  are  plentiful  is  variously  estimated  at  from  $6  to  $10.  A  like 
number  of  worms  can  be  killed  with  an  insecticide  at  a  cost  of  not 
more  than  $2  or  $3  an  acre — sometimes  less. 

THE    USE   OF   PARIS   GREEN. 

In  some  districts  of  Kentucky  Paris  green  has  been  in  use  for  over 
a  decade.  In  the  dark-tobacco  districts  of  Kentucky  and  Tennessee 
it  certainly  was  used  to  some  extent  10  years  ago  and  at  the  present 
time  is  in  very  general  use.  On  account  of  the  frequent  injury  to 
tobacco  by  the  use  of  this  insecticide  many  farmers  would  not  use  it 
if  labor  could  be  secured  to  do  the  hand-picking.  On  the  whole,  the 
cost  of  the  Paris  green  plus  the  cost  of  application,  plus  the  loss 
due  to  damaged  tobacco,  is  much  less  than  the  cost  of  hand-worming. 
In  this  district  the  use  of  insecticides  has  come  to  stay.  It  is  a  neces- 
sity. 

Paris  green  is  applied  with  a  dust  gun  and  without  a  carrier. 
From  1  to  2  pounds  per  acre  is  the  usual  application;  1  pound  when 
worms  are  small  (i.  e.,  less  than  half  grown)  and  2  pounds  when 
there  are  many  worms  over  half  grown.  Success  with  the  applica- 
tion depends  upon  the  judgment  of  the  farmer  in  choosing  the  time 
of  application  and  upon  the  thoroughness  with  which  the  application 
is  made.  Much  of  the  tobacco  that  is  injured  by  Paris  green  is  in- 
jured because  of  unevenness  of  application,  or.  what  is  too  frequently 
the  case,  because  the  grower  has  delayed  the  application  until  half- 


IB8SNATB  01     LEAD    LQAIN81     N>BACG0    HOBNWOBM  8 

grown  or  two-third-  ^rmvn  worms  haw  become  dangerously  nn- 
merous,  and  has  then  put  <»n  a  large  and  uneven  application  with  the 
bope  thai  he  would  kill  all  the  large  worms.  Thia  is  an  example  of 
poor  judgment.  Two  applications  Bhouid  have  been  made.  '1  l>  • 
first  should  have  been  smaller  and  at  an  earlier  date  in  order  to  kill 
the  worm-  while  small,  and  also  to  lessen  the  danger  of  burning  the 
tobacco.  The  second  application  should  follow  as  soon  as.  worms 
ii  to  increase  in  numbers  after  the  first  application. 

OBJECTIONS  TO  TH]     PS]    01    PABIS  QB1  i  n  . 

DA1TOI  B     K)    T1IK    OH  KOOIi. 

There  is  occasionally  Borne  injury  or  irritation  to  the  operator  in 
applying  Paris  green.  Wherever  Paris  green  strikes  the  tender 
parts  of  the  body  irritation  soon  occurs  unless  a  thorough  bath  be 
taken  promptly,  Bleeding  at  the  uose  sometimes  occurs  as  ■  result  of 
the  irritation  to  the  mucous  membranes,  For  these  reasons  many 
people  dislike  to  apply  Paris  green.  However,  if  care  is  taken  to 
work  in  a  direction  quartering  the  breeze  and  upon  the  windward 

Bide  of   the   row    while   making   an   application,   a    thick   sack   around 
the  body   and   a   sponge  over   the   UOSC   will   be    found   to   he  excellent 

preventives  of  irritation,  particularly  if  followed  by  a  hath. 

IN.ICKY     BY    PABIS    (iBK.KN     TO    TOBACCO. 

The  very  general  complaint  of  loss  d\n'  to  Pan-  green-burned  to- 
bacOO  has  been  found  to  be  justified.  Under  favorable  weather  con- 
dition- 9  pounds  of  Pari-  green  per  acre,  sometimes  more,  may  be 
applied  without  noticeable  injury.  On  the  other  hand,  unfavorable 
weather  condition-  will  frequently  cause  injury  to  follow  an  appli- 
cation of  only  1  pound  per  acre.  Very  hot  -uns  and  low  humidity 
for  an  extended  period  will  produce  a  condition  of  the  tobacco  plant 
very  susceptible  to  Paris-green  bum.  Light  rains  or  very  heavy 
.lews  immediately  following  an  application  will  wash  the  Pan-  green 
down  into  the  axil-  of  the  leaves  or  into  the  furrows  along  the  mid- 
ribs, and  serious  injury  i-  likely  to  result. 

In  the  Clarksville  district  of  the  dark-tobacco  belt  of  Kentucky 
and  Tennessee  Paris-green  burn  was  quite  severe  during  l'.'ll  and 
1912,  particularly  so  in  L912.  Previous  to  these  years  one  of  the 
most  careful  growers  in  this  district  informed  the  writers  that  his 
I..--  on  a  6-acre  field  of  tobacco,  due  to  Palis-green  burn,  amounted 
lo  8  per  cent  gross,  which  WSS  a  lo--  of  at  lea-t  If.  per  cent  of  the  net 
profit,  and  that  many  other  growers  suffered  a  similar  lo--  in  1912. 
In  1911  the  writer.-  observed  many  fields  in  which  the  loss  equaled 
or  exceeded  that  quoted  above.  In  L912,  however,  the  injury  by  Paris 
green  was  more  widespread  than  for  several  year-,  notwithstanding 


i 


4  ARSENATE   OF   LEAD   AGAINST   TOBACCO   HORN  WORMS. 

the  fact  that  many  growers  who  suffered  loss  the  year  before  were 
extremely  careful  in  making  applications. 

On  January  4,  1913,  the  senior  writer  interviewed  several  tobacco 
buyers  employed  by  the  Italian  Government.  He  was  informed  that 
several  crops  of  tobacco  the  grade  of  which  was  especially  suitable 
for  the  Italian  Government  were  not  bid  upon  because  of  the  large 
percentage  of  tobacco  injured  by  Paris  green.  The  buyer  stated  that 
for  one  crop,  had  it  been  in  average  condition  in  regard  to  Paris- 
green  injury,  he  would  have  bid  8^  cents  per  pound.  In  its  damaged 
condition,  however,  he  did  not  believe  the  crop  was  worth  over  5 
cents  per  pound — a  gross  loss  of  3^  cents  per  pound,  or  of  $25  to  $30 
per  acre.  Another  crop  would  have  received  an  offer  of  8  cents  per 
pound  from  the  Italian  buyers,  but  on  account  of  Paris-green  burn  no 
offer  was  made.  This  buyer  thought  the  crop  worth  not  more  than 
5|  cents — a  gross  loss  of  2^  cents  per  pound,  or  about  $20  per  acre. 
A  third  crop  had  its  value  reduced  by  one-half,  a  fourth  crop  was 
apparently  worth  about  5  cents  per  pound,  and  would  ordinarily  have 
brought  9  cents.  This  is  the  report  of  buyers  of  the  heavier  types  of 
tobacco  grown  in  this  district.  The  lighter-bodied  tobaccos  undoubt- 
edly suffered  as  severely  and  probably  more  severely  than  the  heavier 
tobaccos,  because  the  lighter  tobaccos  are  ordinarily  more  susceptible 
to  Paris-green  injury. 

Paris  green  injures  tobacco  in  two  ways:  First,  by  causing  dead, 
burned  areas  upon  the  leaves,  where  the  powder  has  been  collected  by 
the  dews  or  washed  down  by  the  rains;  second,  by  weakening  the  leaf 
at  the  stalk.  Light  rains  wash  the  insecticide  into  the  axils  of  the 
leaves,  and  the  result  is  that  many  leaves  drop  off  before  cutting  time 
or  become  so  weakened  that  they  drop  off  when  the  plant  is  cut. 
Such  leaves  are  not  a  total  loss,  for  they  are  collected  and  cured,  but 
they  are  a  partial  loss.  They  are  light  in  weight  and  lack  gloss  and 
elasticity. 

THE  USE  OF  ARSENATE  OF  LEAD. 

Arsenate  of  lead  causes  none  of  the  injury  mentioned  above.  Ex- 
periments performed  under  the  direction  of  the  senior  writer  showed 
that  powdered  arsenate  of  lead  may  be  put  on  a  fresh  sucker  wound 
in  large  quantities  without  causing  any  noticeable  injury,  and  that 
when  applied  to  a  torn  or  bruised  leaf  it  produces  no  injury.  Paris 
green  can  not  be  applied  to  tobacco  in  the  "graining"  stage  (i.  e.. 
when  nearly  ripe)  in  sufficient  quantities  to  do  good  insecticidal  work 
without  too  grave  danger  of  burning  the  plant.  Arsenate  of  lead,  on 
the  other  hand,  can  be  safely  applied  to  tobacco  in  the  "  graining  " 
stage  in  quantities  sufficient  to  produce  satisfactory  insecticidal  re- 
sults.    Furthermore,  arsenate  of  lead  will  cause  no  irritation  to  the 


ARSENATE    0]     LEAD    A0AIN81     rOBACCO    BOBNWOBM8. 

operator  as  will  Puis  green;  in  feet,  thus  far  it  bee  produced  do 
Doticeable  injurious  effects  upon  the  operators. 

Since  arsenate  of  lead  can  be  applied  t"  tobacco  without  injuring 
Hie  plant,  and  since  it  i>  very  much  lees  objectionable  from  tin-  oper 
■tor's  standpoint,  its  insecticide!  properties  Bhould  next  !>»■  disci 
A-.  the  dosage  end  action  <>f  Paris  green  arc  irerj  widely  known,  the 
value  of  arsenate  ol  lead  as  an  insecticide  can  the  more  easily  In* 
explained  by  comparing  it  with  Pans  green.  I  In-  following  tables 
will  serve  t'>  Bhos  the  relative  values  of  the  two  insecticides  under 
different  conditions. 

Tabli  I.-  Comparison  of  fAe  Insecticidal  effects  against  horweortns  of  arsenate 
of  lead  and  Parte  grean  In  f'ii>  w athi 


I 'ile  of 
ftppU  ttkn 

s 

B.d 

o  » 

2 

a 

3 

V. 

Poison  used. 

K  summations  to  (hem  number  ol  worm-  killed. 

3 

o 
V. 

g 
- 

a 

On  day 

-'1- 

pttad. 

On  flm 

day 
alter. 

and 

day 

after, 

On 

third 

on 
fourth 

after 

on 

Oftb 

day 

;ifl>T. 

5   . 

'ft'S 
„1 

°a 

1 

E 
= 
2 

d 
> 

< 

1 

a 

d 
> 

< 

1 

Q 

d 

■o 

•: 

> 

< 

1 

d 

< 

d 
- 

d 

< 

a 

1 

".1910 

Aiu-    J4    19111 
1    1911 

1,1911 

s 

1 

I-ead  arsenate. 



Paris  green. 

Paris  green 

134 

130 
106 
135 
107 

0 
0 
0 
5 
7 

40 

7.1 

h 

80 

56 
61 
49 
45 
17 

M 

35 
14 
70 
61 

29 
SI 

17 
30 
lo 

'14 

50 

3 

5 
35 
50 

: 
23 

15 

(») 

(») 

50 

4 

31 

i 

100 

s 

100 

1  Taken  on  200  plants  by  ordinary  band-worming. 
>  Uiuiy  small  worms  alire. 

Arsenate-of-lead  experiments  Nos.  1  and  2  wen1  applied  under 
Very  favorable  conditions,  i.  e.,  there  was  dew  upon  the  plants  and 
do  breeze.  Paris-green  application  No.  3  was  applied  under  equally 
favorable  conditions.  These  three  experiments  killed  worms  very 
satisfactorily.  The  records  in  Table  I  were  made  by  counting  the 
worms  on  60  plants  of  tobacco  on  each  succeeding  day  after  the  ap- 
plication. No.  1,  5-pound  dosage  of  arsenate  of  lead,  gave  th>- 
best  results,  for  on  the  fourth  day  after  the  application  only  2  live 
worms  were  found  in  hand-worming  200  hills.  The  3J-pound  dosage 
of  arsenate  of  lead  was  not  quite  so  good,  although  only  14  live  worms 
were  found  on  200  plants  the  fourth  day  after  the  application.  The 
Paris-green  application  No.  3  killed  more  quickly  than  either  of  the 
applications  of  arsenate  of  lead,  but  on  the  fifth  day  after  the  appli- 
cation numerous  small  worms  were  noticed  in  worming  200  plants. 
It  was  thus  apparent  that  the  Paris  green  was  losing  it>  effect,  owing 
to  heavy  dews  which  tended  to  puddle  it.  and  to  heavy  drying  winds 
during  the  day.  which  blew  some  of  it  from  the  plants. 

The  application  in  experiment  No.  4  was  not  made  under  the  nm-i 
favorable  conditions.     There  was  a  slight  breeze  during  the  appli- 


J 


G 


ARSENATE   OF    LEAD   AGAINST    TOBACCO    HORN  WORMS. 


cation;  in  addition,  there  were  a  large  number  of  eggs  on  the  plants, 
and  many  of  the  young  worms  hatching  from  these  eggs  were  not 
killed  until  they  wandered  from  the  place  of  hatching.  The  same 
is  true  of  experiment  No.  5,  the  lf-pound  dosage  of  Paris  green.  It 
will  be  seen,  however,  that  experiment  No.  4,  the  arsenate-of-lead 
application,  was  more  effective  than  the  Paris-green  application,  for 
on  the  day  of  application  there  were  at  least  140  worms  in  experi- 
ment No.  4,  the  arsenate-of-lead  application,  and  only  114  worms  in 
experiment  No.  5,  the  Paris-green  application,  while  on  the  fourth 
day  after  the  applications  there  were  only  31  live  worms  in  experi- 
ment No.  4,  but  52  in  experiment  No.  5. 

The  poisons  were  applied  in  the  following  series  of  tests  in  the 
morning  from  6.30  to  9  o'clock.  The  arsenate  of  lead  was  mixed  with 
an  equal  weight  of  dry  wood  ashes.  All  applications  were  made  with 
fan  dust  guns.  The  mixture  of  ashes  and  lead  arsenate  made  a  very 
good  dust  and  compared  favorably  in  evenness  with  the  application 
of  Paris  green.  Rain  began  to  fall  at  11.30  a.  m.  and  continued  in- 
termittently until  2  p.  m.  Part  of  the  rain  was  dashing.  About  one- 
third  of  an  inch  fell.  The  first  examination  of  the  plats  was  made 
after  3  p.  m.  of  the  same  day.  The  tobacco  on  these  plats  was  nearly 
full  grown  and  lapped  in  the  rows  considerably. 


Table    II. — A    comparison    of    the    iiixvcticidal    effects    against    hornworms    of 
arsenate  of  lead  and  Paris  green  in   rainy   weather. 


Date  of 
application. 

Dosage. 

Poison  used. 

Examinations  to  show  number  of  worms 
killed. 

6 

a 

a 

On  day 
applied. 

On  first 
day 
after. 

On 

second 

day 

after. 

On           On 
third       fourth 

day         day 
after.    1    after. 

Size  of 
worms  left. 

g 

R 

> 
< 

OS 

o 

a 

d 

> 

< 

•o 

8 

a 

> 

< 

a 

© 

> 

< 

■a      9 
a      .C 
a      — 

O      < 

3 

a 

1 

Auk.  2R.1911 
do 

do 

Pound* 
ptracrf. 

5 

4 

2J 

Lead  arsenate. 
do 

59 
102 

87 

49 
21 

15 

15 

4S 

54 

41 

27 

29 

10 

21 

34 

8 
13 

14 

6 

33 

36 

2 

8 

9 

Small. 

2 

Small      and 

3 

Paris  green 

medium. 
Small    to 

large. 

The  three  experiments  recorded  in  Table  II  are  very  interesting. 
They  show,  first,  that  arsenate  of  lead  was  far  more  effective  during 
rainy  weather  than  was  Paris  green  (see  number  of  live  worms  on 
the  fourth  day),  even  though  a  very  heavy  dosage  of  Paris  green 
was  used;  second,  that  to  be  very  effective  during  rainy  weather  an 
application  of  at  least  5  pounds  of  arsenate  of  lead  per  acre  is  re- 


ARSI  \  u  I    "I     LEAD    IGAINS1     rOBACCO    HORN  WORMS.  7 

quired.  Experiment  No.  ■_'.  I  pounds  of  arsenate  of  lead  per  acre, 
more  affective  than  the  -'.  pounda  of  Piris  green.  AJthough  a 
oonaidefable  Dumber  of  worms  were  left  on  plat  B,  we  Bnd  thai  fewer 
were  alive  in  this  experiment  on  the  fourth  day  than  were  slive  in 
the  Paris  green  experiment,  notwithstanding  the  fad  that  there  weir 
practically  20  per  cent  more  worms  on  No.  B,  the  arsenate  of  lead 
plat,  at  the  time  of  application  of  the  poison  than  there  were  mi  the 
Pari-  green  plat.  Fortunately  for  the  effect  upon  the  tobacco  plants, 
the  rain  washed  off  nearly  all  the  Paris  green,  so  that  there  was  eery 
little  burning.  There  was  do  burning  of  plant-  on  the  arsenate  of 
lead  plats. 

Tun i-  in.    CotHpOfiwK  of  tnaectMSol  effect  "f  pood  mill  poor  application*  i>f 

111  N-  miti    nj   b  ad. 


Dateof  appti- 

lon. 

- 

c 

8 

KxniuiimiiutLs  to  Bad  numbef  of  worms 
killed. 

6 

M 
- 

Day 

ap- 

pltod. 

i  M 
after. 

■li  v 

Thinl 

after 

M 

! 

£ 
> 

5 

— 

■d 

«J 

— 
- 

3 

\ 

1 

Aug.   16,1910 
Aug.  25,1910 

4 

31 

33 

0 
0 

N 

61 

41 
35 

u 

e- 

11 

I. Ill"                                       -i     pUllls 

■     50   plants 
(•our. 

2 

•  U 

i 

On 

201 

pla 

n!-^. 

Ill  T;»l>le  III.  which  gives  a  comparison  Of  S  good  and  I  poor  ap- 
plication of  arsenate  of  lead,  application  \o.  l.  41  pounds  arsenate 
of  lead  per  acre,  was  from  the  sump  keg  as  application  No.  2,  •"•', 

pounda  per  acre.  Counts  were  made  on  .">()  hills  in  each  instance. 
On  Augu-t  10,  IB10,  many  eggs  were  noticed  on  the  plants,  90  that 
most  of  the  worms  appearing  on  this  plat  were  small.  It  will  be 
noticed  that  the  application  did  not  keep  down  the  increase  of  WOlTOS 
due  to  hatching.  In  experiment  No.  2  there  were  very  few  eggs  "ii 
the  plants  and  the  worms  were  therefore  larger  than  on  plat  1  and 
harder  to  kill.  Practically  a  clean  sweep  was  made  on  No.  •_'.  only 
1  [  worms  heing  found  on  200  plants  on  the  fourth  day  after  the 
application.  Favorable  weather  prevailed  after  both  applications, 
and  the  conditions  at  the  time  of  application  to  both  plats  were 
equally  favorable.  What.  then,  is  the  explanation  of  the  poor  results 
on  plat  1  and  of  the  very  excellent  results  on  plat  •-'  *.  The  explana- 
tion is  found  in  the  carrier.  In  No.  1  the  arsenate  of  lead  WBS  mixed 
thoroughly  with  an  equal  weight  of  finely  sifted  air-slaked  lime, 
while  in  No.  2  it  was  thoroughly  mixed  with  an  equal  weight  of 
finely  sifted  dry  wood  ashes.     Notwithstanding  the  dryness  of  the 


A 


8  AB6ENATE   OF    LEAD  AGAINST   TOBACCO   HORNWOBMS. 

lime  the  mixture  lumped  out  of  the  gun  considerably.  On  the  other 
hand,  the  arsenate  of  lead  and  ashes  made  a  very  even  dust,  with 
scarcely  any  lumping.  These  two  experiments  are  here  shown  to 
emphasize  the  necessity  of  applying  a  thoroughly  even  dust.  A 
lumpy  application  is  a  waste  of  time  and  material  and  will  be  no 
more  effective  than  would  a  perfect  application  which  had  been 
rained  upon  immediately  following  the  application. 

HOW  TO  APPLY  ARSENATE  OF  LEAD  TO  TOBACCO. 

Paris  green  is  generally  applied  to  tobacco  by  means  of  a  dust 
gun  and  without  the  admixture  of  a  carrier.  On  the  other  hand, 
arsenate  of  lead  must  be  mixed  with  a  carrier  in  order  to  secure  an 
even  and  thorough  distribution.  Several  carriers  have  been  tested 
with  this  insecticide.  Finely  sifted  air-slaked  lime,  to  our  surprise, 
did  not  dust  evenly.  Road  dust  and  land  plaster  proved  to  be  too 
heavy.  The  best  results  were  obtained  with  finely  sifted,  freshly  burned 
wood  ashes.  At  least  an  equal  bulk  of  the  wood  ashes  should  be  used. 
Mix  the  arsenate  of  lead  and  ashes  very  thorough]}'  and  apply  while 
there  is  dew  upon  the  tobacco  and  when  there  is  no  breeze.  Even  if 
very  dry  and  finely  sifted  ashes  are  used,  unsatisfactory  results  will 
be  obtained  unless  the  application  is  made  with  a  powerful  dust  gun. 
The  hand-power  dust  guns  now  in  general  use  do  not  furnish  suffi- 
cient power  to  make  anything  like  a  satisfactory  and  effective  appli- 
cation. Special  guns  that  will  perform  satisfactory  work  are  gradu- 
ally coming  on  the  market.  The  new  guns  have  a  fan  with  a  diame- 
ter of  8  inches,  whereas  the  old  guns  have  a  fan  diameter  of  only  6 
inches.  The  new  guns  have  also  an  auxiliary  dust  chamber,  which 
is  very  essential,  because  the  dust  containers  of  the  old  guns  are  so 
small  that  they  have  to  be  refilled  five  or  six  times  for  each  acre 
dusted.  Two  refillings  of  the  new  guns  will  be  sufficient  for  dusting 
an  acre. 

To  secure  the  best  results  dust  the  tobacco  when  dew  is  upon  the 
plants  and  when  there  is  no  breeze.  By  reference  to  Table  III  we 
see  the  comparative  results  of  a  good  and  a  poor  application  of 
arsenate  of  lead.  The  use  of  a  carrier  that  does  not  dust  evenly,  the 
application  of  the  insecticide  when  there  is  too  much  breeze,  and  the 
use  of  too  small  a  dust  gun  are  all  certain  to  give  unsatisfactory 
results.     Avoid  these  mistakes,  and  satisfactory  results  will  be  secured. 

Thoroughness  of  application  can  not  be  too  strongly  recommended. 
When  tobacco  worms  are  numerous  a  poor  application  of  an  insecti- 
cide will  miss  worms  enough  to  ruin  in  two  days  more  than  enough 
tobacco  to  pay  for  the  whole  application.  Make  the  application 
thorough. 


LRSENAT]     .'I     LEAD    \..\l\si     rOBACCO    B0BNW0RM8.  B 

ran  qrao]   or   umnui   01    1 1  vD  10  t  n   loainsi    red    pobao 

BORN  Hi,  UU, 

\r  1 1  ,:  if  lead,  theoretically,  ere  either  triplumbic  or  diplumbic, 
although  many  of  tlic  grades  and  brands  are  undoubtedly  a  mixture 
of  the  (\\<>.  Numerous  experiments  by  agents  of  the  bureau  I iu \ •• 
proved  thai  triplumbic  arsenate  of  lead  is  a  very  unsatisfactory 
insecticide  for  use  against  tobacco  bornworms;  in  fact  the  in 
ridal  action  of  thi>  grade  is  bo  slow  that  ?erj  few  growers  would 
p(  an  application  as  ;i  gift.  On  the  other  hand,  an  arsenate  of 
lead  composed  almosl  entirely  of  the  diplumbic  form  produces  very 
satisfactory  insecticidaJ  results  when  used  against  this  insect. 

In  both  the  triplumbic  and  diplumbic  forms  the  arsenic  i-.  present 
as  arsenic  acid.  Theoretically  triplumbic  arsenate  of  lead  in  pow- 
dered form  contains  25.58  per  cent  of  arsenic  acid,  while  the  diplum- 
bic, in  powdered  form,  contains  theoretically  88.15  per  cent  of 
arsenic  acid.  Tobacco  growers  should  demand  a  powdered  arsenate 
of  lead  that  is  composed  largely  of  the  diplumbic  form.  In  order  to 
be  certain   that   the  diplumbic   form   is   predominant  buy  only  those 

powdered  arsenates  of  lead  which  the  manufacturers  will  guarantee 
to  contain  at  least  :W  per  cent  of  arsenic  acid:  also  insist  upon  a 
guaranty  of  not  more  than  1  per  cent  of  free,  or  water-soluble,  arseni- 
OUS  acid,  in  order  to  he  sure  that  the  applications  will  not  burn  the 
tobacco.  The  writers  advise  growers  and  dealers  who  may  use  or 
handle  powdered  arsenate  of  lead  for  use  against  tobacco  worms  to 
demand  a  written  guaranty  that  the  composition  of  the  products  is 
as  recommended  above. 

WHEN  TO   APPLY   ARSENATE  OF  LEAD. 

The  first  application  of  arsenate  of  lead  should  be  made  when 
tobacco  worms  become  too  numerous  to  be  kept  off  tobacco  by  the 
hand-picking  that  is  usually  done  while  hoeing,  Buckering,  or  topping 
tobacco.  In  some  years  B  BOCOnd  and  even  a  third  application  may 
be  necessary.  The  time  for  making  these  applications  will  be  indi- 
cated by  the  numbers  of  eggs  and  young  worm-  appearing  on  the 
tobacco. 

\GK.    OK    ARSENATE   OF    LEAD    RK.QIIRK.I). 

When  tobacco  is  small  and  has  not  begun  to  lap  in  the  row  an 
application  of  8J  pounds  of  arsenate  of  lead  per  acre  will  be  efficient. 
Full-grown  tobacco  should  receive  not  Less  than  5  pounds  per  acre. 
In  water  spray  use  8  to  4  pounds  of  powdered  arsenate  of  lead  per 
100  gaUons  of  water. 


A 


10  ARSENATE   OF    LEAD   AGAINST   TOBACCO    IKiKXWOEMS. 

COST  OF  ARSENATE   OF    I.KAI). 

The  special  grade  of  powdered  arsenate  of  lead  recommended  for 
use  on  tobacco  will  cost  about  22  cents  per  pound  at  the  factory  in 
100-pound  kegs.  The  freight  will  be  about  1  cent  per  pound,  mak- 
ing the  total  cost  23  cents  per  pound  to  the  grower.  Therefore  a  3£- 
pound  dosage  will  cost  about  SO  cents,  while  a  5-pound  dosage  will 
cost  $1.15.  A  2-pound  dosage  of  Paris  green  costs  from  50  to  55 
cents,  while  a  dosage  of  1]  pounds,  which  is  the  smallest  which  should 
be  applied,  will  cost  about  31  to  35  cents.  If  the  comparative  cost 
of  Paris  green  and  arsenate  of  lead  were  the  only  question  to  be  con- 
sidered, it  would  be  useless  to  recommend  arsenate  of  lead.  The 
cost,  however,  for  the  careful  grower  should  be  a  matter  of  strictly 
secondary  consideration.  The  certainty  of  not  burning  the  tobacco 
should  more  than  compensate  for  the  extra  cost  of  this  insecticide. 

SUMMARY. 

Paris  green  frequently  burns  tobacco  very  severely,  and  may 
reduce  the  value  of  the  crop  as  much  as  50  per  cent  in  exceptional 
cases. 

It  is  impossible  to  apply  an  effective  dosage  of  Paris  green  without 
risk  of  burning  tobacco. 

Paris  green,  which  is  applied  in  dust  form,  is  used  at  a  dosage  of 
from  1  to  2  pounds  per  acre. 

Arsenate  of  lead  is  safe  and  effective  during  rainy  weather,  while 
Paris  green  is  dangerous  and  ineffective. 

It  is  recommended  that  arsenate  of  lead  be  used  against  the  tobacco 
hornworms,  and  that  it  be  applied  as  a  dust  or  powder. 

The  dosage  of  arsenate  of  lead  in  powdered  form  varies  from  3$ 
pounds  per  acre  to  5  pounds  per  acre.  If  applied  as  a  spray,  use  3 
to  4  pounds  in  100  gallons  of  water. 

Arsenate  of  lead  applied  in  powdered  form,  as  here  recommended, 
must  be  mixed  with  a  carrier.  The  best  carrier  found  so  far  is  dry 
wood  ashes,  used  in  a  bulk  at  least  equal  to  the  arsenate  of  lead. 

In  applying  arsenate  of  lead  use  a  dust  gun  having  a  fan  diameter 
of  at  least  8  inches. 

Apply  arsenate  of  lead  when  there  is  no  breeze  and  when  dew  is 
on  the  plants. 

Approved : 

James  Wilson. 

Secretary  of  Agriculture. 

Washington,  D.  C,  February  (J.  1913. 


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UNIVERSITY  OF  FLORIDA 


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